The present invention relates to electronic devices, e.g., an organic solar cell, an organic EL a light-emitting electrochemical device, a thin film secondary battery, and a gel actuator, for performing energy conversion in the junction interface between different substances, and a method of manufacturing the same.
When conventional organic solar cells perform energy conversion, incident light produces excitons in a light absorption layer, and these excitons diffuse to the junction interface to perform charge separation. Therefore, as many excitons as possible must reach the junction interface.
Since, however, the actual diffusion length of excitons is at most a few nm, excitons produced in a region far from the junction interface cannot reach the interface. On the other hand, the light absorption coefficient of an organic absorption layer made from an organic dye is approximately 10xe2x88x924 cmxe2x88x921. Therefore, excitons are believed to be produced in a region to a depth of 1 xcexcm from the light-receiving surface. From these facts, it is expected that in an organic solar cell having a flat junction interface, only about a few % of produced excitons actually contribute to photoelectric conversion. At present, the conversion efficiency of organic solar cells having a flat junction interface is at most about 1%.
Recently, a wet organic solar cell using an optical reaction of a ruthenium complex on the surface of a fine titanium oxide grain with a grain size of 100 nm or less has been developed, and a photoelectric conversion efficiency of about 10% is obtained. However, since the system of the device is of wet type, the device still has a problem in portability.
Also, in organic EL devices enthusiastically studied for practical use in recent years, carrier injection from an electrode into an organic thin film is a rate-determining step. Therefore, an interface structure by which as many carriers as possible can be injected from an organic thin film is desired.
In electrochromic display devices or light-emitting electrochemical devices, ions existing in one of layers on the both sides of the interface are moved to the other by applying a voltage across the two terminals of the device, thereby performing display or emitting light. In these devices, the path through which the ions reach the interface is a rate-determining step. Accordingly, the current display or light emission rate is at most a few seconds to a few tens of seconds.
Field emission devices make use of a cold cathode capable of emitting electrons at around room temperature by sharpening the tips of the emitter electrode. Sharpening the emitter electrode requires a mask process. A spint type cold cathode having one sharp portion on the emitter electrode surface for each opening is a representative example of emitter electrodes obtained by a mask process. Another method of obtaining pointed portions of the emitter electrode is to disperse fine particles on the emitter surface and use these fine particles as masks during the course of mask processing. In this method a plurality of pointed portions are formed on the emitter electrode surface for one opening.
In gel actuators, diffusion of molecules to the gel surface is a rate-determining step, so the current driving speed is at most a few seconds to a few tens of seconds.
In thin film secondary batteries, the amount per unit area of ions stored on the electrode surface during charging and the efficiency of diffusion of ions from the electrode surface have an influence on the electrode capacitance density. Therefore, it is effective to form an electrode surface with a structure efficient for ion diffusion, as well as to increase the electrode surface area.
These conventional organic thin film devices as described above have the following problems.
In organic solar cells with a solid junction structure having a flat junction shape, the thickness of a light absorption layer necessary to effectively absorb incident light differs from the length of a free path through which excitons produced by the light absorption can reach the interface. This adversely affects improvements of the photoelectric conversion efficiency. Also, wet organic solar cells in which fine particles form an interface have a problem in portability although a high conversion efficiency can be obtained.
In organic EL devices, the efficiency of injection of electrons or holes from an electrode into an organic thin film is low, and this has an adverse effect on improvements of the luminous efficiency.
In field emission devices, mask process is required for sharpening the emitter electrodes, especially a spint type cold cathode has one sharpened portion for each opening. A process for removing fine particles is required at the end of mask process in which the fine particles are used. Thus the emitter electrode having as many sharpening portion as possible in each opening, can be produced with minimum steps, is desired.
In electrochromic display devices, light-emitting electrochemical devices, and gel actuators having a flat interface shape, the rate of diffusion of ions or organic molecules to the interface has an adverse effect on improvements of the device operating rate. In electrochromic display devices, light-emitting electrochemical devices, and gel actuators in which the interface has a fine particle structure, it is impossible to effectively secure the path of diffusion of ions or organic molecules to the interface. This adversely affects improvements of the device operating rate.
Furthermore, in thin film secondary batteries having an electrode surface shape with disordered micropores, the ion diffusion path is inefficient. This adversely affects improvements of the electrode capacitance density.
The present invention has been made in consideration of the above conventional problems and has as its object to provide an electronic device whose practicality is improved by efficiently performing energy conversion between an organic thin film and an adjacent layer or electron emission from an emitter.
It is another object of the present invention to provide a manufacturing method effective to obtain this device.
Firstly, the present invention provides an organic thin film device comprising a first electrode, an organic material containing layer formed on the first electrode, and a second electrode layer formed on the organic material containing layer, wherein a contour shape of an interface to an adjacent layer in a section of the organic material containing layer has a Hausdorff dimension D falling within the range 1.5xe2x89xa6Dxe2x89xa62.0.
Secondly, the present invention provides a method of manufacturing an organic thin film device comprising a first electrode, a first organic material containing layer formed on the first electrode, a second organic material containing layer formed on the first organic material containing layer and a second electrode formed on the second organic material containing layer, wherein the first and second organic material containing layers are formed by mixing two types of organic materials and separating the organic materials by applying at least one of an electric field, a magnetic field, irradiation of light, a temperature gradient, and a centrifugal force, and a contour shape of an interface in a section of the first and second organic material containing layers has a Hausdorff dimension D falling within the range 1.5xe2x89xa6Dxe2x89xa62.0.
Thirdly, the present invention provides a field emission device comprising a substrate, an electron emitter layer regularly formed on the substrate, an insulator layer formed in a region except for the emitter on the substrate, and a gate electrode layer formed on the insulator layer, wherein a Hausdorff dimension D of a sectional contour shape of a surface of the electron emitter layer falls within the range 1.7 less than Dxe2x89xa62.0 at a scale length of 100 nm to 1 xcexcm.
In the present invention, an interface having a desired Hausdorff dimension and a desired scale length is formed in a thin film for performing energy conversion. Consequently, it is possible to improve the energy conversion efficiency of an electronic device, e.g., improve the photoelectric conversion efficiency of an organic solar cell and the luminous efficiency of an organic EL device, lower the electron emission voltage of an emitter, and also improve the display rate of an electrochromic display device, the light emission rate of a light-emitting electrochemical device, the operating rate of a gel actuator, and the electrode capacitance density and the current density of a thin film secondary battery.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.